A conventional reciprocation type linear driving actuator, for example, shown in Japanese Laid-Open Patent Publication No. 2002-176758 is explained referring to FIG. 15. In this conventional reciprocation type linear driving actuator 150, a plunger 151 formed of a magnetic material is fixed on an outer periphery of a shaft 152. The shaft 152 is pivoted by a bearing 162 capable of reciprocally and linearly moving in a direction (axial direction) parallel to the center axis thereof. A ring shaped coil 154 is disposed on an inner peripheral surface of a shielding case 153 with a predetermined clearance with respect to the outer periphery of the plunger 151. Furthermore, ring shaped permanent magnets 155 and 156 which are magnetized in symmetrical with respect to the coil 154 are disposed on the inner peripheral surface of the shielding case 153 and on both sides of the coil 154 in the above axial direction. Ring shaped first yokes 157 and 158 are respectively disposed between the permanent magnets 155 and 156 and the coil 154, and ring shaped second yokes 159 and 160 are disposed at positions opposite to the permanent magnets 155 and 156 with respect to the coil 154. A spring member 161 is disposed between the plunger 151 and the shielding case 152 (SIC: correctly 153) for applying an accompanying force to the plunger 151 in a one direction among the reciprocation directions of linear driving.
When no current flows in the coil 154, the plunger 151 is stopped at a position where magnetic forces applied to the plunger 151 by two permanent magnets 155 and 156 via the yokes 157 and 158 is balanced with a pressing force due to the spring member 61 (SIC: correctly 161). When a unidirectional current flows in the coil 154, magnetic flux due to one of the permanent magnets 155 and 156 is weakened, so that the plunger 151 moves toward the other permanent magnet against the pressing force of the spring member 161 or with charging the spring member 161. When reverse current flows in the coil 154, the plunger 151 moves to a reverse direction. Therefore, it is possible to reciprocally oscillate the plunger 151 in the axial direction by flowing alternating current in the coil 154.
However, in the above-mentioned conventional reciprocation type linear drive actuator 150, the permanent magnets 155 and 156 are disposed with the clearance with respect to the outer periphery of the plunger, so that inside diameter and outside diameter of the ring shaped permanent magnets 155 and 156 become larger, and volumes of the permanent magnets 155 and 156 also become larger. Following to this, the cost of the permanent magnets 155 and 156 in material becomes expensive. Furthermore, since the permanent magnets 155 and 156 are formed as the ring shape by combination of a plurality of arc-shaped permanent magnets, manufacturing process of the ring shaped permanent magnets 155 and 156 becomes complicated, and the cost of them in manufacturing becomes expensive. As a result, the costs of the actuator using the conventional permanent magnets and coil and the power toothbrush using the same become expensive. Still furthermore, since the permanent magnets 155 and 156 are larger, it is difficult to realize the miniaturization and weight saving of the actuator 150 and the power toothbrush using the same.